1. Technical Field of the Invention
The present invention relates to a key switch pressing a contact which is built into an input part of switch provided in equipment such as a telephone, a mobile communications device, an acoustic instrument, remote controls and an on-vehicle device.
2. Related Art
A push button switch of the telephone or the like is comprised of a key top which the operator touches with a finger at the time of pressing the push button switch and an extruding part (or push stud) pushing a contact member.
As a material of the key top, a rigid resin which has a good feeling of touch and is easy to push is preferably used, and a great variety of key tops may be designed.
The contact member, such as a metal belleville spring with clicking touch, a resin film dome or the like, is placed underneath the extruding part.
FIG. 5 shows an example of conventional push button switches having key tops made of rigid resin. In this case, the key tops 5 made of thermoplastic resin are firmly fixed to keypads 7 made of silicone rubber having extruding parts 6 via adhesives 8. FIG. 6 shows another example of conventional push button switches wherein key tops 5 made of thermoplastic resin having integrally shaped extruding parts 6 are firmly fixed by means of a resin film 9.
In conjunction with miniaturization of telephones, portable terminals or the like, there is a growing demand for reduction in size of push button switches. However, in the former conventional push button switch, because the key tops are one by one fixed to the keypads by means of the adhesives, the manufacture of such a push button switch requires much time and trouble, which resulting in the difficulty in the miniaturization thereof.
On the other hand, in the latter conventional push button switch, the extruding parts are also made of resin with a high rigidity. For this reason, in case where the contact member is a metal belleville spring, a pressing load at the time of clicking is heavy, and the load is applied to a substrate placed underneath the metal belleville spring, which results in the occurrence of dent marks on the surface of the substrate. Further, in case where the contact member is a resin film dome, the load is applied to the dome, thereby causing the decrease of the clicking touch of the contact member and the crack of the contact member due to the concentration of residual stress. Moreover, there has been a problem in that in case of linking a plurality of key tops, adjacent key tops are operated together when one of the key tops is pressed.
For the purpose of solving the above-mentioned problems, the present invention provides a key switch in which by forming an extruding part by elastic material different from a rigid resin of a key top, the clicking touch of a contact member may be improved, and breakage and laceration of the contact member may be prevented, and further miniaturization of a push button switch may be facilitated.
More specifically, a key top made of thermoplastic resin and an extruding part made of thermoplastic elastomer are integrated into one body. Preferably, a plurality of key tops are connected by integrating their extruding parts by means of a bridging member. Further preferably, a decorative layer composed of a paint coating or a metal coating is formed on the surface of a key top.